1. Field of the Invention
The present invention relates generally to a steering column apparatus constituting a steering apparatus for an automobile, etc., and more particularly to a technology of smoothly fastening and releasing an inner column when adjusting a telescopic or axial position of a steering wheel.
2. Related Background Art
A steering apparatus of an automobile is used by a multiplicity of unspecified drivers, and it is therefore desired that a position of a steering wheel be adjustable corresponding to an individual physique, a driving posture, etc. For meeting such demands, there are an increase in a number of freight cars, etc., adopting a tilt adjusting mechanism and/or a telescopic position adjusting mechanism, without being limited to the passenger cars.
The tilt adjusting mechanism is a mechanism for adjusting the position of the steering wheel in up-and-down directions. The tilt adjusting mechanism is constructed of a tilt pivot for supporting a steering column in a rotatable manner, a tilt fixing member for fixing the steering column in a desired position (at a desired tilt angle), and so on. Further, the telescopic position adjusting mechanism is a mechanism for adjusting the position of the steering wheel in front-and-rear directions (in axial directions of a steering shaft). The telescopic position adjusting mechanism is constructed of a double tube type extensible/retractable unit including an outer column and an inner column that are used for extending and retracting the steering column, and of a telescopic position fixing member for fixing the inner column in a desired position (in a desired extended/retracted state).
A general type of conventional telescopic position fixing member is that the outer column is formed with slits, and the inner column is fixed by reducing a diameter of the outer column by a screw mechanism. There appears, however, a telescopic position fixing member, wherein the inner column is seized by pressure and thus fixed by press blocks held by the outer column. The latter telescopic position fixing member is constructed of, for example, as shown in FIG. 10, a lock housing 15 formed at a rear side end of an outer column 3, a pair of left and right press blocks (first and second press blocks 21, 23) slidably held downwardly of the lock housing 15, a fastening bolt 71 screwed into the first press block 21, a nut 75 screwed on the fastening bolt 71, and a fastening lever 35 fixed to the nut 75. Then, the two press blocks 21, 23 become proximal to or separated away from each other by rotating the fastening lever 35, whereby the inner column 5 is fixed or released (refer to, e.g., Japanese Utility Model Registration No.2588338).
The telescopic position fixing member disclosed in Japanese Utility Model Registration No.2588338 has a problem that will hereinafter be explained. For instance, this telescopic position fixing member has a drawback, wherein the first and second press blocks 21, 23 are driven by the screw mechanism, and hence, if an operating force of the driver is too large for fastening by the fastening lever 35, the two press blocks 21, 23 are intruded onto the inner column 5, resulting in a plastic deformation of the inner column 5. Further, the two press blocks 21, 23 move in the horizontal direction along an axis of the fastening bolt 71, and therefore, in case an operation quantity of the fastening lever when performing a releasing operation is small, it follows that moving quantities of the two press blocks 21, 23 with respect to the inner column 5 become also small. In this case, the inner column 5 is not perfectly released and is brought into the press-contact with the two press blocks 21, 23, with the result that the operation of adjusting the telescopic position might not be smoothly conducted, and that scratching or biting might occur when performing the telescopic position adjusting operation.